Fix a test failure on 32-bit systems.

Taken from upstream:
https://gitlab.freedesktop.org/mesa/mesa/commit/dd1dba80b9ee74ec8b90761285a8262e374bf8ef

diff --git a/src/util/tests/timespec/timespec_test.cpp b/src/util/tests/timespec/timespec_test.cpp
--- a/src/util/tests/timespec/timespec_test.cpp
+++ b/src/util/tests/timespec/timespec_test.cpp
@@ -206,7 +206,7 @@ TEST(timespec_test, timespec_from_nsec)
 
    timespec_from_nsec(&a, UINT64_MAX);
    EXPECT_EQ(a.tv_nsec, UINT64_MAX % NSEC_PER_SEC);
-   EXPECT_EQ(a.tv_sec, UINT64_MAX / NSEC_PER_SEC);
+   EXPECT_EQ(a.tv_sec, (time_t)(UINT64_MAX / NSEC_PER_SEC));
 }
 
 TEST(timespec_test, timespec_from_usec)
